An IGBT (Insulated Gate Bipolar Transistor) has been employed in a power semiconductor device. In a case where the IGBT is used as a switch, it is desirable that an ON-state resistance be low, and a switching speed be high.
When a gap of trench gates of the IGBT becomes narrow, an n type base region provided between the trench gates is increased in resistance. Therefore, an IE (Injection Enhanced) effect is generated, and the ON-state resistance of the IGBT becomes small.
However, the aspect ratio of the trench gate becomes high as the gap of the trench gates becomes narrow, and the manufacturing of the IGBT becomes difficult. Furthermore, when the trench gate is shallow, the IE effect is reduced, and the ON-state resistance is increased.